25,845 research outputs found

    Three Dimensional Topological Field Theory induced from Generalized Complex Structure

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    We construct a three-dimensional topological sigma model which is induced from a generalized complex structure on a target generalized complex manifold. This model is constructed from maps from a three-dimensional manifold XX to an arbitrary generalized complex manifold MM. The theory is invariant under the diffeomorphism on the world volume and the bb-transformation on the generalized complex structure. Moreover the model is manifestly invariant under the mirror symmetry. We derive from this model the Zucchini's two dimensional topological sigma model with a generalized complex structure as a boundary action on ‚ąāX\partial X. As a special case, we obtain three dimensional realization of a WZ-Poisson manifold.Comment: 18 page

    Effect of in-plane line defects on field-tuned superconductor-insulator transition behavior in homogeneous thin film

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    Field-tuned superconductor-insulator transition (FSIT) behavior in 2D isotropic and homogeneous thin films is usually accompanied by a nonvanishing critical resistance at low TT. It is shown that, in a 2D film including line defects paralle to each other but with random positions perpendicular to them, the (apparent) critical resistance in low TT limit vanishes, as in the 1D quantum superconducting (SC) transition, under a current parallel to the line defects. This 1D-like critical resistive behavior is more clearly seen in systems with weaker point disorder and may be useful in clarifying whether the true origin of FSIT behavior in the parent superconductor is the glass fluctuation or the quantum SC fluctuation. As a by-product of the present calculation, it is also pointed out that, in 2D films with line-like defects with a long but {\it finite} correlation length parallel to the lines, a quantum metallic behavior intervening the insulating and SC ones appears in the resistivity curves.Comment: 16 pages, 14 figure

    Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer

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    We investigated the relationship between tunnel magnetoresistance (TMR) ratio and the crystallization of CoFeB layers through annealing in magnetic tunnel junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C, whereas the TMR ratio of the MTJs with pinned layers without Ru spacers decreased at Ta over 325C. Ruthenium spacers play an important role in forming an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through annealing at high temperatures.Comment: 10 pages, 5 figures, submitted to Applied Physics Letter

    Theoretical Description of Resistive Behavior near a Quantum Vortex-Glass Transition

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    Resistive behaviors at nonzero temperatures (T > 0) reflecting a quantum vortex-glass (VG) transition (the so-called field-tuned superconductor-insulator transition at T=0) are studied based on a quantum Ginzburg-Landau (GL) action for a s-wave pairing case containing microscopic details. The ordinary dissipative dynamics of the pair-field is assumed on the basis of a consistency between the fluctuation conductance terms excluded from GL approach and an observed negative magnetoresistance. It is shown that the VG contribution, G_{vg}(B=B_{vg}, T \to 0),to 2D fluctuation conductance at the VG transition field B_{vg} depends on the strength of a repulsive-interaction between electrons and takes a universal value only in the ordinary dirty limit neglecting the electron-repulsion. Available resistivity data near B_{vg} are discussed based on our results, and extensions to the cases of a d-wave pairing and of 3D systems are briefly commented on.Comment: Explanation of data in strongly disordered case, as well as Fig.2 and 3, was renewed, and comments on recent publications were added. To appear in J.Phys.Soc. Jp

    QP-Structures of Degree 3 and 4D Topological Field Theory

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    A A BV algebra and a QP-structure of degree 3 is formulated. A QP-structure of degree 3 gives rise to Lie algebroids up to homotopy and its algebraic and geometric structure is analyzed. A new algebroid is constructed, which derives a new topological field theory in 4 dimensions by the AKSZ construction.Comment: 17 pages, Some errors and typos have been correcte

    Josephson Vortex States in Intermediate Fields

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    Motivated by recent resistance data in high TcT_c superconductors in fields {\it parallel} to the CuO layers, we address two issues on the Josephson-vortex phase diagram, the appearances of structural transitions on the observed first order transition (FOT) curve in intermediate fields and of a lower critical point of the FOT line. It is found that some rotated pinned solids are more stable than the ordinary rhombic pinned solids with vacant interlayer spacings and that, due to the vertical portion in higher fields of the FOT line, the FOT tends to be destroyed by creating a lower critical point.Comment: 12 pages, 3 figures. To appear in J.Phys.Soc.Jpn. 71, No.2 (February, 2002

    AKSZ-BV Formalism and Courant Algebroid-induced Topological Field Theories

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    We give a detailed exposition of the Alexandrov-Kontsevich-Schwarz- Zaboronsky superfield formalism using the language of graded manifolds. As a main illustarting example, to every Courant algebroid structure we associate canonically a three-dimensional topological sigma-model. Using the AKSZ formalism, we construct the Batalin-Vilkovisky master action for the model.Comment: 13 pages, based on lectures at Rencontres mathematiques de Glanon 200

    An Alternative Topological Field Theory of Generalized Complex Geometry

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    We propose a new topological field theory on generalized complex geometry in two dimension using AKSZ formulation. Zucchini's model is AA model in the case that the generalized complex structuredepends on only a symplectic structure. Our new model is BB model in the case that the generalized complex structure depends on only a complex structure.Comment: 29 pages, typos and references correcte
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